Average Fuel Economy

[Quitsa]

I have built a custom engine gauge display page. One of the data box choices that I selected is "average fuel economy." Although the real-time live combined fuel economy works fine, the average one stays blank. A related question is that the "average fuel economy" option for a data box in the sidebar is not available to select even though it is available for the gauge page. That seems odd.

So what's the story with the "average fuel economy'? It would be a nice thing to have.

 

[Sparky Wire]

Do you have tank sensors installed on this boat?

 

[Quitsa]

Yes I do but that should not have any bearing on the calculation because I use the manual fuel management function. The tank gauges bounce around a lot inevitably when the boat is underway and the virtual tank level from the manual gauge is much more accurate since it uses the actual fuel rate from the engines to calculate remaining fuel based on the fuel level user input.

 

[Sparky Wire]

Normally fuel information is setup based on real tank information or manual configuration, but not both. Manual configuration is just a calculation of your input values using the fuel rate information from the engines. Unless you setup everything for using real measured values, there are likely going to be some data that isn't available. If the fuel tanks bounce around a lot, maybe the tank sensors have a smoothing setting which used to balance that out.

 

[Quitsa]

It's not just that the tank level readings bounce around, it's that they will change with the trim of the boat. Sitting at the dock or at displacement speed when the trim is level, they read accurately. But at planing speed with the boat running at a 4-5 degree bow up angle, the gauges read high because the sensors are in the aft portion of the tanks. Add in the effect of going up and down waves and the transient inaccuracy becomes quite large.

It's easy enough to change settings back and forth so maybe I will try using the tank data instead of manual fuel management and see what happens.

I am just using "Manual Fuel Management" by the way. There isn't any way to use both as far as I can tell.

 

[Johnny Electron]

Like sparky says, if you have tank sensors it is more accurate to use real data (as long as all the data is good) to calculate the fuel.

 

[Quitsa]

Like sparky says, if you have tank sensors it is more accurate to use real data (as long as all the data is good) to calculate the fuel.

I don't understand why that would be the case. If the correct starting value is entered in manual fuel management and you update as fuel is added, it is far more accurate than relying on an imprecise tank sensor because it is using the fuel consumption from the engine ECU to calculate remaining fuel. So today for example I started out with 300 gallons and used 84 per my engine gauges and the manual fuel management tank level showed 216 gallons remaining in the tanks. My tank readings from the sensors are not nearly as precise.

 

[allrelative]

So what does “average” really mean?

• Is it the average for the entire trip?
• The last 30 seconds?
• The past 10 minutes?
• Or since the last reset?

When you're riding up the back of a wave, fuel economy drops. When you're surfing down a following sea, it improves dramatically.

With my Volvo EVC system, the real-time fuel economy readings are extremely accurate, which helps make sense of these fluctuations.
I will look for the average and add it, see how well that works.
here is mine. Total fuel is top right.

 

[Quitsa]

My Cummins Diesels also provide real-time fuel consumption, which I can display just as you have done. What I had in mind was a resettable trip average that divided nautical miles travelled by total fuel burned. I can do the calculation myself since my engine gauges have a resettable total fuel consumed display and the TZT3 has a trip odometer. Yesterday I ran 89 miles and burned 80 gallons of fuel or 1.11 nmpg average fuel economy. It would be nice if there was a data box showing that number, especially for long tri

 

[allrelative]

I get it now and yes that would be interesting.
A simple fuel used since powered on OR fuel used per day would suffice.